The invention relates to a capacitor having a signal electrode connected to a signal conductor and a ground electrode connected to a ground conductor. The capacitor further has a dielectric layer with a high dielectric constant provided between the signal electrode and the ground electrode.
Tubular or through-connection capacitors are known, as well as chip capacitors which, having appropriate capacitance values, are used as filter capacitors. The capacitance values and dielectric strength of these capacitors can in this case in general be set to the desired values, but, when such capacitors are in use, particularly with dielectrics having high dielectric constants, at high frequencies (above about 103), delay time effects limit the usage options. These limits occur where such delay time effects do not allow the capacitor to be charged simultaneously over its entire plate area.
It is accordingly an object of the invention to provide a capacitor that overcomes the disadvantages of the prior art devices of this general type, in which the delay-time-dependent limit is moved to a higher frequency range, in order to extend the applicability in the frequency range under this.
With the foregoing and other objects in view there is provided, in accordance with the invention, a capacitor, including a signal electrode that is subdivided into at least two conductor regions that are separated in a direction of signal propagation, a ground electrode, and a dielectric layer having a high dielectric constant that is disposed between the signal electrode and the ground electrode. A signal conductor and a plurality of conductor connectors are provided. At least one of the conductor connectors is disposed between and electrically connecting each of the two conductor regions of the signal electrode to the signal conductor such that the signal conductor is spaced apart from the signal electrode and thus from the dielectric having the high dielectric constant. Finally, a ground conductor is connected to the ground electrode.
Alternatively, the capacitor includes a ground electrode that is subdivided into at least two conductor regions being separated in a direction of signal propagation, a signal electrode, and a dielectric layer having a high dielectric constant that is disposed between the signal electrode and the ground electrode. A ground conductor and a plurality of conductor connectors are provided. At least one of the conductor connectors is disposed between and electrically connecting each of the two conductor regions of the ground electrode to the ground conductor such that the ground conductor is spaced apart from the ground electrode and thus from the dielectric having the high dielectric constant. Finally, a signal conductor is connected to the signal electrode.
In order to achieve the objective, the signal conductor or the ground conductor is disposed such that it runs at a distance from the plates. With this configuration, the high dielectric constant of the dielectric of the capacitor (dielectric constant approximately in the range from 103-2xc3x97104) can no longer exert any influence on the conductor, and the propagation speed of the signal on the conductor is not reduced. Generally, even a relatively short air gap is sufficient for this purpose. The signal conductor or the earth conductor thus do not run on the dielectric of the capacitors having a high dielectric constant, but in a medium with a low dielectric constant (dielectric constant approximately in the range from 100-101) and the propagation speed on the freely running signal conductor or ground conductor corresponds to that in air. It can thus be regarded as being xe2x80x9cunderlayedxe2x80x9d, while the propagation speed when in contact with the dielectric is considerably reduced, owing to the high dielectric constant.
In this case, one of the electrodes (the signal or ground electrode) which is associated with the conductor that is at a distance from the dielectric material is subdivided in the direction of signal propagation into individual conductor regions, which are electrically insulated from one another. The conductor regions are electrically connected via in each case one separate connecting conductor to the conductor which is at a distance from the dielectric, so that the electrically mutually insulated conductor regions are connected like a parallel circuit, seen from the signal or ground conductors. Since the signals propagate without any delay on the signal conductor or the ground conductor disposed at a distance from the dielectric, the signal voltages appear virtually simultaneously at the connecting conductor associated with a capacitor, so that the individual conductor regions are charged and discharged (virtually) simultaneously. Owing to this xe2x80x9csimultaneityxe2x80x9d, delay time differences are suppressed, and their disturbing influence region is shifted toward higher frequencies. Each conductor connector is advantageously connected roughly in the form of a point to the associated signal conductor or ground conductor. This connection is advantageously disposed in the center of the conductor. In this case, the term xe2x80x9ccenterxe2x80x9d is the center, lying in the propagation direction of the signals of the conductor region. This type of connection ensures (virtually) simultaneous charging and discharging of the capacitor subdivided in such a way.
In order to allow the electrical characteristics to be influenced, the mutually insulated conductor regions are connected via electronic components like a series circuit. Resistance elements, preferably purely non-reactive resistors, may be provided as components in this case. Since the propagation speed of the signals on the signal conductor or the ground conductor is dependent on the dielectric constant of the material surrounding the conductor, and owing to the discontinuities which occur when resistors are connected in conductors carrying signals, the resistance values of the resistors should be in the region of the characteristic impedance of the signal conductor or the ground conductor which is interacting with the dielectric having the high dielectric constant. This configuration ensures that discontinuities caused by connection are kept small.
The individual plates of the capacitor which are associated with the signal conductor are, in a development, connected via electrical components, for which purpose resistors, varistors or the like may be used. Surface mounted components are advantageously provided as the resistance components, which are soldered onto two adjacent conductor regions, represent a bridge, and electrically connect the two adjacent conductor regions to one another via the resistor, like a series circuit. In another embodiment, strips of resistance pastes that are known from planar technology are applied, for example, using the screen-printing method are provided. The resistance pastes form resistance components, which connect two adjacent conductor regions to one another. Varistors are suitable to achieve voltage limiting, in particular peak-voltage limiting in the case of surge loads, in which case the value of the limiting voltage can be achieved by suitable varistor selection or the varistor-like material.
In addition to resistors of a purely non-reactive nature, inductive elements can also be provided for connection of the signal conductors or of the ground dissipation conductors, as a result of which the non-reactive resistors also contain an inductive component. For this purpose, the signal conductor or the ground conductor is connected to at least one inductance. Surface mounted coils may be connected into the signal conductor or the ground dissipation conductor as inductances. Alternatively, layers or rings composed of a ferritic material may also be provided on the signal conductor or the ground dissipation conductor for this purpose.
In one advantageous development, inductances are provided between at least some of the connecting points of the conductor connectors of two successive conductor regions of the signal or ground electrodes which are subdivided into the individual conductor regions. Surface mounted coils may be connected in the signal conductor or ground conductor as inductances. Alternatively, beads or rings composed of a ferritic material may also be provided on the signal or ground conductor in this case, and these are advantageously disposed in the region between the subdivided plates. The configuration results in filters with parallel-connected parallel-path capacitors, which are connected via series-path inductances. The filter characteristics of such configurations may be matched to the requirement by choice of the ring material and/or of the capacitors. In addition, it is also possible to insert inductive componentsxe2x80x94for example surface mounted coilsxe2x80x94in the freely running signal conductor or ground conductor, which are then connected in series for signal connection or ground connection.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a capacitor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.